Moss is a common sight on trees in the wild. It can look gorgeous, and in your garden, it is what can give it a forest feel. However, it also poses a risk.
Not from the moss, but the water it holds.
Moss thrives in wet conditions. The wetter the moss gets, the heavier it becomes.
Too much moss blanketing trees can see branches snap off, and trunks become weak. When storm season rolls around, that is when the risk is more severe.
How to remove moss from trees?
Moss can be removed by hand or the gentle pressure of a garden hose. Mature trees may require a soft setting of a power washer. Chemical controls include copper sulfate, lime sulfur, or potassium salt. Once removed, keep trees pruned to increase sunlight, which prevents moss from settling.
Chemicals that kill moss high up on trees
For mature trees, the height may make it difficult to safely remove the moss from high up on a tree.
When you cannot reach the moss safely to manually scrape it off, the next best solution is to kill it so that it falls off.
Two chemicals are effective at killing moss. Copper sulfate and lime sulfur. These are what professional companies use however, they are toxic to all plants and should only be applied to trees over the winter period when they are dormant.
Should copper sulfate be used, care should be taken to control chemical drift as this is not only toxic to all plant life but is also corrosive. Protection from drift should be considered for nearby paintworks, such as on homes, garden buildings, and painted metal fencing.
A safer alternative is potassium salt for moss control.
This is the most widely available algaecide sold at garden centers for use in home gardens.
The bottles usually have a hose-end attachment so you can attach the garden hose to the bottle then direct the spray onto the moss on the tree.
It will start to work instantly, but can take a few days to be absorbed by the moss.
Once the moss dies back, it becomes easier to remove. A soft brush can be used to knock off dead moss.
Manually scrape away moss that is within reach
As moss is a bryophyte that uses short rhizoids to cling to bark, it can easily be scraped or picked off by hand. Provided it is within reach.
On shorter trees and shrubs, this is all that is required to remove moss. Rub a gloved hand over it to loosen either carpet mosses coating branches or clump mosses growing on branches and twigs.
The lack of roots on all types of moss is what makes it extremely easy for kids to learn about how to grow moss indoors. Consider harvesting some for a fun side-project.
Wash it off with a hose
A garden hose is sufficient for spraying moss off of trees, provided it is not too high up. Pressure or power washers are not recommended for removing moss from trees because the pressure removes the bark too.
For comparison, a regular water faucet delivers approximately 50 PSI (Pounds per Square Inch). It can be higher and regulators can be applied to the faucet to lower the pressure.
How much of that pressure reaches plants, trees, and shrubs depends on the length and diameter of the hose, the type of nozzle, the setting it is used at, and the distance the water is sprayed from.
As an example, a faucet with a garden hose on a jet spray setting would exert more pressure up close than a nozzle with the setting set to sprinkle.
Power washers amplify pressure, which is why they are not recommended for cleaning trees. A pressure washer delivering 2,000 PSI will debark trees. At that force, it would damage the canopy too, tearing tender foliage and destroying buds.
When using water to spray moss off of trees, only use a garden hose. Too high a pressure will strip the outer layer of the bark, exposing the phloem to fungi and bacteria. The damage could be irreversible.
Use a garden hose on young trees. On mature trees, pressure washers may be used, but always on the gentlest setting and with the hose-end sprayer kept at a distance to reduce the force.
The less forceful the water impact has on the bark of a tree, the less damage it can do.
Prune trees to prevent moss from accumulating
Moss is not like most plants. It longs for wet, damp, and dark(ish) conditions. The moister the branches, the more likely it will be for moss to form.
For that reason, the simplest method to prevent moss growth is to increase natural sunlight and boost air circulation so the bark dries faster.
Pruning trees is how to keep moss, algae, and lichens from anchoring on the bark. This is easier on young fruit trees that are often pruned to produce more fruits anyway.
On tall mature trees with overarching branches and a dense canopy causing the trunk to be layered in a thick carpet of moss, it raises the question of where do you cut plants when pruning?
Thinning cuts (which are taking branches back to the trunk) are the ones to focus on to increase light penetration and reduce the overall canopy denseness. Reduction cuts are only recommended on young trees to control growth.
Once the height is there, it is safer to cut branches back to the trunk rather than to reduce the trunk size directly.
Frequently Asked Questions related to removing moss from trees
Does moss need to be removed from trees?
Moss does cause direct damage to trees. The indirect damage is caused by the excessive weight strain it puts on tree trunks and branches. It can hold as much as 10x its weight in water content. During storms, the weight can become too much, increasing the risk of branches breaking off from trees.
How often do chemicals need to be applied to keep moss from returning?
On mature trees that are too tall to be safely pruned, chemical controls will only kill active growing moss. While the conditions remain moist and shaded, moss will return. To keep moss to a minimum, repeat chemical treatments will be needed every few years.
Marcel runs the place around here. He has a deep passion for houseplants & gardening and is constantly on the lookout for yet another special plant to add to his arsenal of houseplants, succulents & cacti.
Marcel is also the founder of Iseli International Commerce, a sole proprietorship company that publishes a variety of websites and online magazines.